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Commercial superphosphates contain 14-20% of PaO6 soluble in water and
citrate; their strength, in percentage of PaO0, is only guaranteed as 14/16,
15/17, 16/18, 18/20. The normal percentage of moisture is 10-15 m mineral
superphosphates and 13-16 in those from bones.

Bone superphosphates contain i-i'5% of organic nitrogen and are to be
regarded as genuine when they contain less than <>M% AUG., + Fe2OB, less
than 0-1% CaFjj, less than 0-05% CaCla, less than i% SUX, less than 0-3% of
residue insoluble in acids, (and this is free from nitrogen) ami no manganese, and
when the value of the ratio CaO : P2()fi lies between 1-30 ami 1-35, that: of SO3
X 100 : total PaOr, is 110-129, and that of SO., X 100 : soluble! Pa(.')G — 110-132
(in the last two ratios SO., and P,jOn are referred to 100 parts of dry sub-

The mineral superphosphates, on the other hand, contain no nitrogen, but
relatively large proportions of alumina and ferric, oxide, fluorine, silica and
insoluble residue ; further the ratio SO,, x 100 : total Pa<'>r, iHi -227 and SO,,
X 100 ; soluble PaOr, ~~ 184--242 (SO., and PaO5 reCerred to dry substance).

Double and triple supc.rphosph.alcs contain 40--45% P./V


Dcphosphorisation slag, or Thomas xltig, forms a. line, brownish-grey
powder, and it. contains calcium phosphate, mostly (75 70% of the total
PaOB) soluble in ammonium citrate or eitrie acid, and on this its value depends.
Analysis of this product comprises the following :

1.  Total Phosphoric Anhydride (L<w's method}.    5 grains of sub-
stance, placed in a 250 c.c. measuring, arc moistened with water, 25-
30 c.c. of cone, sulphuric; acid added, and the llask, covered with a funnel,
heated on a gauze or sand-bath until white vapours are emitted ;  (he liquid
is then diluted with water, allowed to cool, up to volume with water
and mixed.   To 50 c.c. of the filtered liquid (•••   i gram of substance) are
added 20 c.c, of ammonium citrate, 50 c.c. of water, 50 e.c. of ammonia
(1) -•••-• 0-92), and 50 c.c. of magnesia, mixture, the procedure (lien being that

•for the ordinary determination of total phosphoric anhydiide \scc General
Methods, 4).

2.  Phosphoric Anhydride soluble In Citric Acid (\Vtinner's method}.
-......-The following solutions are required :

(a)  Citric Acid.   100 grams of the crystallised acid and 0-05 grain of
salicylic acid are dissolved in water to I litre.    Immediately before use, I
vol; of this solution is diluted with 4 vols. of water, this giving the 2% citric
acid solution necessary for the determination.

(b)  Molylidic solution.    150 grams of pure ammonium molybdate are
dissolved in 500 c.c. of water and the solution poured into i litre of nitric
acid (!) rig), 400 grams of ammonium nitrate being added, the volume
made up to 2 litres with water, the liquid left at about 35" for 24 hours and
then filtered.

(c)  Magnesia, mixture.   This is prepared as indicated on p. 123.

5 grams of slag, in a graduated  500  c.c.  flask,  are  moistened with
5 c.c. of alcohol and the volume made up, gradually and with thorough-
shaking, with the 2% citric acid solution.    It is then rotated mechanicallyital., 1898, p. 270) ; F. Martinotti: "A Method for Distinguishing Bone Phog